Sous Vide Bags and Vacuum Sealing: How to Seal Food Safely
By Dana Cole | Reviewed by Chef Daniel Pryce
Published · Last reviewed · 4 min read
Key takeaways
- Two methods work: a vacuum sealer, or zip-top bags using the water-displacement method, which costs nothing extra to start.
- Use food-grade bags only; the goal is an airtight seal so the food sits in full contact with the water.
- Floating bags lift food out of the water and cook it unevenly, so trapped air is the real problem to solve.
- Keep bags submerged with a clip or weight, and check the seal before the water comes up to temperature.
You can bag food for sous vide two ways: with a vacuum sealer, or with a zip-top freezer bag using the water-displacement method, and both work as long as the seal is airtight and the food sits in full contact with the water. The bag is not glamorous, but it is where most beginner cooks go wrong, so it is worth getting right. Here is how I think about it after years of both methods.
Vacuum sealer vs water-displacement method
Both methods aim for the same thing (an airtight bag with the air removed), so the choice is about convenience, not results. A vacuum sealer draws the air out mechanically and heat-seals the bag, which is fast and very reliable, especially for long cooks or batch meal prep. The water-displacement method uses a sturdy zip-top freezer bag and the pressure of the water itself to push the air out, and it costs nothing beyond bags you may already own. For everyday cooking at the gentle temperatures sous vide uses, often 130 to 165°F (54 to 74°C) per reputable charts1, either method holds up fine. I cooked on zip-top bags for the better part of a year before I bought a sealer, and my steaks were no worse for it.
How the water-displacement method works
You seal all but a corner of a zip-top bag, lower it slowly into the water, and let the rising water pressure squeeze the air out before you close the last corner. Put the seasoned food in a food-grade freezer bag, zip it almost shut, then dip it into the bath keeping the open corner above the surface. As the water climbs, it presses the bag tight against the food and forces the air out through that gap; when the bag clings and the air is gone, seal the corner. The danger zone for food is 40 to 140°F (4 to 60°C)2, so do not let bagged raw food sit out at room temperature while you fiddle; work quickly and get it into the bath. For more on managing the bath itself, see our water-bath tips.
Bag safety and food-grade materials
Use only food-grade bags rated for cooking temperatures, and pick sturdy freezer-style or vacuum-seal bags rather than thin sandwich bags. Most sous vide stays well below boiling, but heat plus time is exactly the combination that matters, so a bag marketed as food-grade for the temperature range is the baseline. Pasteurisation in sous vide depends on time and temperature together, not temperature alone, and the bag’s only job is to keep the food sealed and in clean contact with the water while that happens; cite Douglas Baldwin and USDA guidance for the times and temperatures, and avoid extended holds below about 130°F (54.4°C)3. If you are cooking for people who are pregnant, very young, elderly, or immunocompromised, the bag is the least of it; cook to standard safe internal temperatures. The full picture is in our food-safety guide.
Floating bags and how to fix them
A floating bag means trapped air, and trapped air lifts the food out of the water where it cooks unevenly, so removing every pocket is the real fix. Air is buoyant; even a small bubble can tilt a bag and leave one edge of a fillet above the surface, cooking it to a different doneness than the rest. First, re-remove the air: with the displacement method, dunk and re-seal; with a sealer, re-seal a leaking bag. Then hold the bag down: clip it to the side of the container, or add a food-safe weight inside or on top. A lid or a layer of water-bath balls also helps on long cooks by cutting evaporation that would otherwise drop the water line. On a 2 to 4 hour steak cook, I clip every bag now after one floated and gave me a grey, half-cooked corner.
Checking the seal before you cook
Check the seal before the water reaches temperature, because a leak found early costs you a bag and a leak found late can cost you the whole cook. Gently squeeze the sealed bag and watch for bubbles escaping or water seeping in at a corner. If a bag leaks, move the food to a fresh food-grade bag and re-seal; do not nurse a failing seal through a multi-hour cook, because water in the bag dilutes seasoning and, over long holds, removes the clean isolation the bag is meant to provide. A reliable seal is also what lets you batch-cook ahead and reheat later, covered in reheating with sous vide. The other gear that makes this easy is explained in equipment explained.
This guide is general information and one cook’s experience, reviewed by a professional chef. Always follow current food-safety guidance for your situation, and cook to standard safe internal temperatures when serving higher-risk eaters.
Frequently asked questions
Do you need a vacuum sealer for sous vide?
No. A vacuum sealer is convenient and gives a very reliable airtight seal, but you do not need one to start. Zip-top freezer bags using the water-displacement method work well: you seal all but a corner of the bag, lower it into the water, and let the pressure push the air out before closing the last corner. Many home cooks, myself included, ran for months on zip-top bags before buying a sealer.
What is the water-displacement method?
It is a way to remove air from a zip-top bag without a vacuum sealer. You place the seasoned food in a sturdy zip-top freezer bag, seal it almost all the way, then slowly lower the bag into the water bath. As the water rises around it, the pressure squeezes the air out through the open corner. Once the air is gone and the bag clings to the food, you seal the final corner above the water line.
Are zip-top bags safe for sous vide?
Use food-grade bags rated for the temperatures you are cooking at, and choose sturdy freezer-style zip-top bags rather than thin sandwich bags. Most sous vide cooking happens at gentle temperatures, often 130 to 165°F (54 to 74°C), well below boiling, but check that the bag is marketed as food-grade. If you cook for higher-risk eaters, the bag choice matters less than cooking to standard safe internal temperatures.
Why does my sous vide bag float?
A floating bag almost always has air trapped inside, or air worked its way back in through a weak seal. Air is buoyant and lifts part of the food above the water, where it cooks unevenly or not at all. Fix it by re-removing the air, double-checking the seal, and adding a clip or a food-safe weight to hold the bag under the surface for the whole cook.
Can you reuse sous vide bags?
Reuse vacuum-seal rolls and zip-top bags only if they held low-risk foods and you can clean them fully, and never reuse a bag that held raw meat, poultry, or fish. The seal also weakens with each use, which invites floating and leaks. When in doubt, start with a fresh food-grade bag; the cost of a bag is small next to the risk of a failed seal on a long cook.
What happens if water gets into the bag?
A leak lets water in and can let bag contents out, which dilutes seasoning and, on longer cooks, raises a food-safety concern because the food is no longer isolated in clean conditions. If you spot a leak early, move the food to a fresh bag and re-seal. If a bag with raw meat leaked for an unknown stretch on a long cook, treat it cautiously and follow standard safe-temperature guidance.
References
- The Food Lab's Complete Guide to Sous Vide, Serious Eats. ↩
- Safe Minimum Internal Temperature Chart, USDA Food Safety and Inspection Service. ↩
- A Practical Guide to Sous Vide Cooking, Douglas Baldwin. ↩
Written by Dana Cole. Reviewed by Chef Daniel Pryce.
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